The present invention relates to data communications equipment and, more particularly, to the detection of a voice signal in a simultaneous voice and data communications system.
The co-pending, commonly assigned, U.S. patent application of Gordon Bremer and Kenneth D. Ko entitled "Simultaneous Analog and Digital Communication," Ser. No. 08/076505, filed on Jun. 14, 1993, describes a simultaneous voice and data communications system in which a voice signal is added to a data signal for transmission over a communications channel to a receiving modem.
In this simultaneous analog and digital communication system, the data signal to be transmitted is represented by a sequence of data symbols, where each data symbol is associated with a particular N-dimensional signal point value taken from a signal space. Similarly, the analog signal, which is represented by a voice signal, is processed so that it is mapped into the N-dimensional signal space to provide a voice signal point. This voice signal point defines the magnitude and angle of a voice signal vector about the origin of the signal space. The data symbol and the voice signal vector are then added together to select a resultant N-dimensional signal point, which is then transmitted to a far-end modem.
Upon reception of the transmitted N-dimensional signal point, the receiver of the far-end modem detects the embedded data symbol and subtracts the data symbol from the received N-dimensional signal point to yield the voice signal vector. This voice signal vector is then used to recreate the voice signal.
Using this above-mentioned technique to simultaneously transit voice and data, the quality of the voice signal is affected by the underlying data rate as described in the co-pending, commonly assigned, U.S. patent application of Gordon Bremer, Kenneth D. Ko, and Luke J. Smithwick, entitled "Shaped Signal Spaces in a Simultaneous Voice and Data System," Ser. No. 08/076530, filed on Jun. 14, 1993. Generally speaking, when transmitting data plus voice the higher the data rate--the lower the quality of voice transmission. This is because at a higher transmission rate, the data symbols are closer together, which results in a lower dynamic range for the voice signal. Therefore, when transmitting a voice signal, it is preferable to reduce the number of symbols in the data signal space in order to increase the allowable dynamic range of the voice signal--which concomitantly improves the quality of the voice transmission.